Gas in rads

[JohnRMoore]

When our system gets nice and hot the rads fill up with an unidentified gas. I burnt some and it had a clear blue flame, orange edges and left soot on the bleed key and molegrips I was holding the key with. Any ideas? It's a brand new boiler and 15yr old rads. Open vented.

 

[PlumbBobBob]

just insist he uses fernox or sentinel that way you will be sure a decent make was used, ok it will cost more but for peace of mind in the long run you can't go wrong really.

 

[JohnRMoore]

If so, have you got a link to show a good general arrangement? He mentioned that the pump would be moved to the vertical and would be pumping down. I know that the pump is just circulating the flow, but I though pumping down hill was just bad practice to be avoided generally? (I bet you plumbers wished the internet had never been invented! What do the say about a little knowledge...)

 

[goz666]

You could ask him to put some calchem 3 in1 in the system while he's fitting the air separator. This stays in permanently and doesn't need flushing out, have had some really good results shifting cold spots with this.

 

[Nostrum]

How often are the rad's filling up with air? If its regularly its drawing air in so either its piped wrong or the pumps set to high for the configuration. It may also explain why it burnt for longer if there is a considerable amount of oxygen in there aswell rather than just a build up of hydrogen.
Air seperaters from my experience, are normally used if you have a low head installs, they shouldn't be required if you have 600mm plus between water level in tank and top of system. Did he fit a new pump?

 

[Howsie]

I think the MI specificies a mains flush and does not mandate a power flush...

 

[smileyplumber]

john it might be worth finding out what the dosage rate was with the inhibitor used ( gold 100 )
there is a limit to the amount of radiators 1 ltr will treat if your system is a large one or many rads then maybe it needs moore inhibitor introducing to the system , perhaps a call to fernox or sentinel or preferably the gold the company used im sure they will have some answers . let us know if you get anywhaere with it , Smiley

 

[congokeith]

hi John is there a differential by-pass fitted? is it possible that an old sledged up micro bore system is not allowing enough flow through the boiler now that its got a new pump? causing it to pump over into the exp. tank. this would allow fresh oxygenated air to enter the system
make sure that the feed and exp. pipework is correctly configured if u used the old pipework the f & e maybe connected across the flow and return, the new boiler may require a close coupled connection using either the flow or return (cant remember which)you said the pump had been moved could be the feed is now on the wrong side
I would get up in the loft and have a look what's going on in the tank
fitting an air ejector will treat the symptoms but wont tell you the cause good luck

 

[JohnRMoore]

Feed tank is in the loft, well in excess of 60mm above system. If I bleed all the radiators it all goes nice and quiet. Starts making the popping noises normally next day. The noise is loudest as the thermostatic heads start to close once the house has heated up in the morning. After a couple of days there is enough gas to create glugging noises. I have tried the pump on its highest setting, and it doesn't seem to create any problems. I have even tried holding a pint glass of water over the vent while my wife switched the system on (a tip i read on the web) - no more that a slight dip in water level - hardly conclusive I know but the pump doesn't seem to be the problem. In fact I can run the system cool for a few days with no problems even with the pump set quite high, it only seem to be when the water gets really hot that the the gas occurs - totally wierd, but in my simple GCSE science mind I imagine the corrosion reaction occurs more quickly at higher temperature. Maybe enough hydrogen bubbles create elasticity in the system which then draws air through the vent as the water can 'slosh' more - how's that for a long shot! PS he didn't fit a new pump.

 

[Nostrum]

Can you take a picture of your controls etc, are you getting any water out of your overflow from your F&E tank particularly when the system is at its hottest??

 

[JohnRMoore]

There is only and on/off switch and a thermostat setting on the front, I was told to leave it at 3/4, but to turn it up in cold weather. I have left it on 3/4.The water level does go up and down in the F&E tank, but never empties and never overflows, although I will check again.

 

[SPH]

hi, microbore central heating system are much harder to power flush as the pipework is much smaller, the powerflush works on the basis of flow and with small bore piping you cant always get the flow through the pipes, you may need to change the piping or change some of the rads, or maybe try a stronger chemical to flush the system poss fx2,
hope this helps

www.shawsplumbingandheating.co.uk

 

[SPH]

Hi, microbore piping is much harder to powerflush as the pipe are much smaller, powerflushing works on the basis of flow and with small bore pipes you cant get the flow through the pipes, you may need to replace the pipework or change the rads or try using a stronger chemical to powerflush the system poss fx2 and the header tank should always be removed and cleaned out otherwise the dirt will just re- enter the system, hope this is helpful.
www.shawsplumbingandheating.co.uk

 

[smileyplumber]

John is there any plastic pipework showing on the system do all the rads have TRV's ( thermostatic rad valves ) fitted if so as asked earlyer on by some one has it got a bye pass valve fitted anywhere

if there is plastic pipe how old is it, and is it a barrier pipe ? because none barrier pipe causes oxygen to be obsorbed into the systems water wich i have known to kill a new boiler withing couple years easily . the bye pass is requierd due to TRV's all shutting down as being upto temp this may cause pumping over to happen.
other than that how old are the rad valves maybe one or more could be sucking air in if they are in a negative presure area of the pump . just a few thoughts
plus what colure is the water within the system clear / black / brown etc ?

 

[JohnRMoore]

The pump is not a new one, but even so the plumber did double check the configuration, and did mention about the possibility of pumping over so I assume he checked for that. I'm glad you mentioned about treating the symptoms coz that's what I'm worried about too!

 

[JohnRMoore]

No plastic pipe, and all TRV's except one in the hallway, and there is a bypass with a gate valve on it. The plumber has looked at this, and recommended that I upgrade from a 3 way to 2 x 3 way valves with an automatic bypass. But it used to be fine! The rad valves are 15 years old, I am guessing. However, since the pump is a few centimeters upstream of the cold feed I am assuming this is the only area that could possibly 'suck' in air? I must admit, it is one particular TRV upstairs that makes a lot of noise, and the same rad that gets most gas - but no negative pressure surely? - the F&E tank is in the loft. PS the water is clear with black flecks and occasional translucent 'floaty' bits!